Silicon nanostructures for thermoelectric devices: A review of the current state of the art

Abstract

Silicon is the most important element of modern semiconductor industry. As a thermoelectric converter material, it would be able to promote applications dramatically since device integration and scaling of the fabrication processes could be borrowed from existing technology. Though the thermoelectric performance of single crystalline silicon is only poor, silicon nanostructures have demonstrated a competitive figure of merit. To make use of these nanostructures, novel device architectures are necessary. This review provides an overview over the physical background of silicon as thermoelectric converter material as well as different nanostructures like nanowires, porous nanomeshes, and nanocrystalline bulk and their thermoelectric properties, focusing mostly on experimental data. Further, different thermoelectric converter device concepts including nanowire device concepts, pn junction thermoelectric generators and integrated spot coolers are discussed and their realization with silicon nanostructures briefly sketched. (a) Nanowires, porous nanomeshes and nanocrystalline bulk with promising thermoelectric material's figure of merit. (b) Innovative device concepts using nanowires or large area pn junctions for thermoelectric heat‐to‐electricity conversion.

Phonon and heat transport control using pillar-based phononic crystals

“…However, the experimentally observed 20% reduction in thermal conductivity is interesting to compare with the reduction obtained in other silicon-based nanostructures. On one hand, a stronger reduction was measured in silicon with pores (>50%) [9,18,19], nanodots (>70%) [13,68], polycrystalline grains (>80%) [15,69,70], dopants (>50%) [71,72] or germanium atoms (>70%) [14,71,73]. On the other hand, the 20% reduction by the pillars [63] is comparable to the reduction by holes (20–25%) [21,74] or slits (20–30%) [75] covering the same relative area.…”

“…Moreover, PnCs can reduce the thermal conductivity [5,6]. Thus, PnCs can enhance the thermoelectric efficiency of poor thermoelectric materials, such as silicon [7–9], and be used in energy harvesting applications [10,11] along with other nanostructured [11–14] and hierarchical [15,16] materials.…”

Dense nanopowder composites for thermal insulation

“…The phonon spectrum is reduced at higher wavelengths and hence a thermal conductivity below the Einstein-level should be attainable [7]. This concept has already led to a much improved figure of merit for thermoelectric devices [8]. We apply a similar approach to thermal insulation materials.…”

Thermal Diffusivity of SPS Pressed Silicon Powders and the Potential for Using Bottom–Up Silicon Quantum Dots as a Starting Material

“…1 While silicon shows a relatively high electrical conductivity and Seebeck coefficient, it is let down by its high thermal conductivity, rendering bulk silicon a poor thermoelectric material (figureof-merit, ZT < 0.01). 2 By comparison, nanostructured silicon materials have been shown to be significantly more successful in terms of ZT.…”